Vacuum brake power boosters are devices which utilize the pressure gradient between the vacuum in the suction pipe of an Otto carburetor engine and the atmospheric ambient pressure as a source of power to boost the hydraulic pressure which is generated in the master cylinder by the foot effort of the driver.
A vacuum pump which is driven by the engine and which furnishes the required vacuum is used, as a rule, in two-stroke engines or Diesel engines.
Vacuum brake power devices of this kind are, among others, described in detail in the Brake Handbook by Alfred Teves GmbH, 8th edition, from page 94 onward.
From the German patent application published without examination, No. 29 35 286, a brake power booster for a vehicle brake unit is known. That booster includes a booster housing having a front and a rear housing wall, a pedal-actuated input member axially aligned with an output member, a movable wall sub-dividing the interior space of the housing into two chambers and suited to apply a force to the output member when the chambers are subjected to a pressure differential depending on the force exerted on the input member, and a power transmission device extending between the front housing wall and the rear housing wall and which, during operation, transmits braking reaction forces which would otherwise be transmitted by the housing.
In the forementioned German patent application published without examination, the power transmission device is provided with a pipe which is coaxial with the input member and with the output member and which extends through the movable wall.
Furthermore, a mechanically controlled brake device for an automotive vehicle is known which includes a master cylinder and a booster utilizing the pressure differential between a vacuum and the atmospheric pressure. The booster has a vacuum housing which includes a cup section and a cover section, a push rod which serves to initiate the braking action, and structure enabling fixation to a splash shield.
The structure for fixation is arranged in the vicinity of the master cylinder, preferably on that side of the cup section which faces the master cylinder.
In addition, FIG. 1 of U.S. Pat. No. 3,137,361 shows a brake power booster whose housing presents a bearing block for the brake pedal.